When was real combat first recorded on film? Probably almost as soon as the "cinematograph" camera was invented. They say that around 1916, Mexican revolutionary general Pancho Villa used to stage battles for his cameramen to record when the light was good. During the second world war, John Ford and John Huston were just two of the great Hollywood directors who picked up 16mm cameras to film real action for, respectively, The Battle of Midway and Report from the Aleutians. But these were straightforward propaganda movies for the most part: they made no pretences of showing what combat was really like for a soldier – what it felt like physiologically and psychologically. Their aim was to stir the patriotic fervour of the audience and to soothe their anxieties about the conflict.

Perhaps it was because of some pang of conscience on his part – for covering up the true human cost of warfare in his films – that Huston later made his heartbreakingly beautiful postwar documentary Let There Be Light. Without sentimentality, it shows the suffering of soldiers after combat, living with what we'd now call post-traumatic stress disorder. The film was banned by the US government for 30 years.

The first documentary I saw that tried to show the actual experience of being a soldier in combat was The Anderson Platoon, by French director Pierre Schoendoerffer, which won the Oscar for best documentary in 1967. It follows a platoon of GIs on patrol in the rice paddies and jungles of south Vietnam, and during a brief – but sex-filled – furlough in Saigon. Although The Anderson Platoon was what we would now call an "embedded film" – with all the ambiguities that term implies – somehow Schoendoerffer got away with showing things as they really were from a grunt's perspective.

Despite the limitations of the bulky 16mm camera and 10-minute film magazines, The Anderson Platoon feels as spontaneous and fresh as any films that have come out of the Afghan or Iraq wars. Here is the chaos of combat, the camera swinging around wildly through the undergrowth, catching the bedlam of a skirmish. Here are close-ups of terrified boys in a state of shock; here are almost comic (if they weren't so tragic) encounters with the local populace who complain that their fields and livestock are being destroyed and, no, they know nothing about the Vietcong; here is a scene of a GI singing a beautiful song to remind him of home. Sometimes the only difference seems to be that back in 1967 the GIs didn't have shoot-'em-up video games, which seem to play an enormous part in every modern soldier's life.

Shot on black-and-white film, often without synchronised sound, The Anderson Platoon feels extraordinarily, almost uncannily, similar to its more modern embedded descendents: Restrepo, Hell and Back Again, which debuted at Sundance in January, and the latest example of the type, the Danish film Armadillo.

There is no doubt that the advent of lightweight, cheap digital cameras has made the filming of combat much easier than it was. We are all now accustomed to the blurry immediacy of "helmet-cams" with their computer game-like first-person point of view. In war films, even more than in other kinds of documentary, we've come to think that shaky, poor-quality footage is somehow more authentic than something classically "well shot". (This rough aesthetic even dominates Hollywood action movies these days, most notably in the Bourne films.) One of the selling points of a film such as Restrepo is how raw it is. If it's this badly shot, the supposition goes, then we must be going to places where a professional film crew can't. It somehow cancels out our natural and justified suspicions of the very concept of "embedded" journalism.

Indeed, one of the major criticisms of Janus Metz Pedersen's film Armadillo is that it is too well made: the poetic quality of the cinematography, colour grading and music supposedly mark the film out as inauthentic. I have to admit that while watching Hell and Back Again, which intercuts an American soldier's combat experiences in Afghanistan with his recovery from PTSD and a leg wound back home, the gorgeous photography (courtesy of the amazing Canon 5D, I would wager, which makes everything look as though it was shot by Ridley Scott) almost made me feel I was watching a drama, and subtly affected my sense of the film's reality.

But what marks Armadillo out is that it achieves a level of thematic clarity and coherence that only the very best documentaries have. The camera always seems to be in the right place at the right time. In the best possible sense, its character development and narrative strength make it feel like a great fiction feature. Unlike other embedded films, it is about so much more than just recording the raw experience of combat. It is a film about the sometimes ugly but undeniable urges that drive men to war, and how the experience of combat is rarely heroic but usually dehumanising.

The film follows a group of young Danish soldiers who have volunteered to serve in Afghanistan at a joint British and Danish fort called Armadillo. Mads, the sensitive but weak central character, starts off by telling his mum that he is going for the comradeship and for "adventure"; we see the word hit her like a ton of bricks.

For the first few weeks the new arrivals complain about being bored. They watch pornography, play practical jokes and get good at computer games. One day, they send up their little spy drone into the air and see three men running between some fields. Somehow they know these are Taliban and call in an artillery strike. The next moment – exactly like something in a Bourne movie – the small black-and-white aerial image we are looking at explodes. There are cheers from the men.

With only a short time left on their posting, our protagonists hear that three Danish comrades, stationed at another fort, have been killed by an improvised explosive device. That night, shaken by the deaths, they are due to go out on a mission to ambush some local Taliban. Unexpectedly (to me at least), the men are asked if they are too upset to go. A few stick up their hands, but most, including Mads, agree to it. They put on warpaint and head to the fields, looking like alien beings in their battle armour and night-vision goggles. Soon they are embroiled in a ferocious fire-fight. It's then, in the midst of the adrenaline, that a group of Taliban are taken out with a grenade, and a possible war crime occurs when the wounded men appear to be machine-gunned to death in a ditch. Mads observes, with horror and confusion, the pumped-up Rambo that his friend Daniel has become in the heat of combat. Daniel shouts, "Die you bastards, die!" as they fire.

That evening, Daniel recounts the incident with undisguised glee. The men pose like tourists with the war booty slung around their necks. It would be easy to condemn them but having seen the film, you understand them – the sadness and fear they felt when their friends were killed, their adrenalin in battle and the consequent flood of relief and joy at a successful mission. Later someone – we suspect Mads – phones home and tells his parents about the alleged atrocity. Rasmus, the patrol commander, is called in by the military police and then summons a meeting of his men, furious that one of them has betrayed the unit. Confronted with the atrocity accusation, the men try to reinvent what happened, uncomfortable now that a name has been put on the experience.

This sequence caused a storm in Denmark. The Danish defence minister was called by parliament to explain the allegations raised by the film. Pederson, the director, refused to be drawn. "Afghanistan is a crazy and complicated place, and I'm no military expert," he told a Danish newspaper. "But I think that most of our resources are going toward military efforts, and we instead ought to focus more on foreign aid than on combat."

"If the press get hold of this and make us look like psychos – well, let them," says one of the soldiers in the film. "They weren't there, they didn't see it. We know what happened." Thanks to Pederson, we were there and we do know what happened, not necessarily in precise legal detail. But we know what war did to these men.